Plastic packages required to have high gas tightness, heat resistance and strength, such as retort pouches, are formed by laminates constituted, for instance, by a film of resins having high heat resistance and high strength, such as polyethylene terephthalate, a highly gas-tight layer such as an aluminum foil, and a sealant layer of cast polypropylene etc. Retort pouches are heated by hot water or a microwave oven, and opened to take out their contents. However, because the pouches have high strength, it is sometimes difficult to open the pouches by hand even if notches are provided on their sides. Particularly as graying population increases people with insufficient grip, there are increasing numbers of people failing to open pouches with notches by hand, sometimes needing scissors.
JP 11-77872 A discloses a method for producing an easy-to-cut laminate film package, comprising irradiating a laminate film comprising a substrate film layer and a sealant layer as thick as ½ or more of the total thickness with laser beams from the sealant layer side, to make the sealant layer thinner, thereby forming a continuous or intermittent half-cut separating line. When a slant, half-cut separating line is formed on a retort pouch by this method, the slant, half-cut separating line should be formed after individual retort pouches are produced, resulting in poor efficiency.
Because stretched films tend to be torn along orientation directions, bags with openings in parallel to orientation directions are easily torn open with notches formed on sides adjacent to the openings. However, such method provides bags tearable only in parallel to openings. Because small openings are preferable in most drinks, fluid foods, etc., packages (bags) with slantly openable portions are desired.